In recent years, from the viewpoints of energy conservation and miniaturization, light emitting devices using light emitting diodes (hereinafter also referred to as “LED”) as light sources, (LED flashes), have been used as light emitting devices for imaging cameras. As the light emitting devices described above, a light emitting device in which an LED and a fresnel lens are combined is well known.
Typically, the shape of an imaging area of an imaging camera is quadrangular. Therefore, in order to obtain a sharp captured image, the light emitting device preferably illuminates an area to be irradiated quadrangularly. Therefore, a fresnel lens to be used for the light emitting device for an imaging camera is required to uniformly and efficiently irradiate the quadrangular area to be irradiated with light emitted from a light emitting element. Also to date, various fresnel lenses have been proposed for illuminating a quadrangular area to be irradiated (see, e.g., PTL 1).
FIG. 1A is a perspective view of fresnel lens 10 disclosed in PTL 1. Fresnel lens 10 illustrated in FIG. 1A can perform the same function as that of cylindrical lens 20 illustrated in FIG. 1B. As illustrated in FIG. 1A, fresnel lens 10 disclosed in PTL 1 includes a plurality of concentric grooves 12 whose shape in plan view is rectangular which are spaced apart from each other.